This invention relates to connectors for communication lines, particularly optical fiber cables.
Because of their great bandwidth, optical communications links seem likely to replace electrical lines for many applications. But optical links require transparent fibers for connections between stations, and such fibers in many ways are more difficult to work with than electrical wires.
Fibers suitable for optical communications applications are usually made of glass or plastic, and tend to be thin and relatively fragile. Therefore, in the design of optical fiber connectors, bend and strain relief are especially important considerations.
In addition, optical fibers which are coupled together must be maintained in both axial and angular alignment with each other to quite close tolerance if light losses are to be kept within acceptable limits.
This would be considerably less difficult to accomplish if it were a problem encountered only rarely and by trained physicists working in a sophisticated laboratory environment. But if optical fibers are to form the basis of a large scale communications network, they must be connected and disconnected often by ordinary personnel working in the field, without the benefit of sophisticated laboratory equipment.
The large number of such operations which will be required dictates that the connectors employed must be manufactured at high volume and low cost, but this must be accomplished without any sacrifice of alignment accuracy.
If these conflicting requirements cannot all be met simultaneously, then either higher cost or degradation of system performance must result. Consequently there is a need for an inexpensively mass-produceable optical fiber connector which is simple for installation and maintenance personnel to use in the field, but which nevertheless produces very accurate and reliable results in terms of fiber alignment.
To complicate the problem further, in many practical applications a number of optical fibers are grouped together in a cable, and should preferably be connected and disconnected as a group. It is too wasteful of time and space to connect and disconnect all the fibers of such a cable by means of individual connectors. Thus it is important that a single connector be able to handle a number of individual optical fibers, but without compromising alignment accuracy as to any of them.
Another problem encountered in the fiber optic connector field concerns the matter of fiber separation. The ends of two optically coupled fibers must approach each other very closely in order to reduce light losses to a minimum. But the two fibers must not be allowed to touch, because then they would grind against each other, destroying the planarity of the polished ends, and generating glass or plastic dust in the light path. Both lack of planarity and the presence of dust are factors which increase the scattering of light, thereby contributing to signal losses. Accordingly, it is necessary to closely control the spacing between the ends of each pair of optically coupled fibers.
Consideration must also be given to problems which may arise during times when the connector is disconnected; at such times the fragile polished ends of the optical fibers may be subjected to the risk of mechanical impact which could cause damage, or may be exposed to dirt or other environmental contaminants which can cut down severely on light transmission. Therefore it is desirable to have a protective cover readily available at all times.
Many prior art fiber optic connector devices employ a double-ended female socket or housing member and a pair of male fiber optic plugs, each of which is inserted within one end of the double-ended socket. Some examples of such connectors are seen in U.S. Pat. Nos. 4,026,633 of Crick, 3,861,781 of Hasegawa, 4,158,477 of Fiebelkorn. But in the past, such double-ended socket connector designs have not gone far enough in combining high accuracy, low light loss, and economy of manufacture. And few, if any, connector designs appear to provide protection for the exposed plugs when they are temporarily disconnected (i.e. withdrawn) from their sockets.